Merchant account recommendation

I've written a little program that I'm sure everyone on the planet is going to want. :bigyello: I will distribute a free trial version that can be registered to operate without the nag screens. What I need is a low-cost merchant account so everyone can pay for their registration code. PayPal is pretty good at this (IPN) but I'm already running a business account through them and don't really want the two to mix so I'm looking elsewhere. Until this thing gets off the ground, I don't want to be paying $25-$35/month for gateway fees, statement fees, etc. and, of course, I'd like a pretty low transaction fee. Most importantly, I need this to all be automated so the purchase can be made online by the customer and the merchant site will talk to my site to tell my database that a valid transaction has occurred.

The question: Does anyone have any recommendations?

Much thanks!